Windows 7: Adding a HDD that already has Win7 on it as an external HDD?

I am getting a new SSD for christmas. I will be installing Windows 7 Ultimate on it doing a fresh/clean install on a new drive.

However, once that is done, I want to connect my old HDD (which was Windows 7 Pro) and get the images and stuff off of it, so I can format it and use strictly for sotrage.

Is it going to cause a conflict? Is this even possible? I don't want to keep the OS on the old HDD. I plan on using that on a different computer.

I don't see it causing any harm since it automatically gets assigned a different drive letter so that no system path points to it anymore.You just copy over what you need, format it the way you want it and go about your business

-DG

Be sure to keep the old HD unplugged during install to SSD, then when you plug it back in you can boot it if needed using BIOS one-time Boot Menu, or just use it as a data drive to copy your data into User folders.

Once you're sure you have everything you need off of it, open an elevated Command Line to wipe the old HD using Diskpart: Disk - Clean and Clean All with Diskpart Command

I think the only time you would have conflict if the SSD and old HDD had the same disk signature. This won't happen given what you are planning (ie. not cloning).
But as Gregrocker says clean install the SSD with it connected alone as disk 0 otherwise you could end having the ssd booting through the old HDD.

And for that same matter disconnect all HDDs. The installer may play an act on you and put the MBR on the first port it finds. I had that happen and the MBR ended up on a data partition of the first HDD it found.